The invention relates to a whip antenna construction having at least two operating frequency bands.
In the world there are cellular communication systems in use that differ from each other significantly in their operating frequency bands. As regards digital cellular systems, the Global System for Mobile telecommunications (GSM) uses frequencies in the 890-960-MHz band, while the Digital Cellular System (DCS 1800) operates at band around 1800 MHz. The operating frequencies of the Japanese Digital Cellular (JDC) system are around 800 MHz and 1500 MHz. The Personal Communication Network (PCN) uses frequency band 1710-1880 MHz, and the Personal Communication System (PCS) frequency band 1850-1990 MHz;. The operating frequencies of the Digital European Cordless Telephone (DECT) system are 1880-1900 MHz. Frequencies in excess of 2000 MHz will be used in new third-generation cellular systems, such as the Universal Mobile Communication System (UMTS). From the user""s perspective it would be desirable that he could use one and the same xe2x80x9cstandard phonexe2x80x9d in these networks if he so wants. A first prerequisite for that is that the antenna of the communications apparatus functions relatively effectively in the frequency bands of more than one network.
Mobile communications apparatus use various antenna constructions, such as e.g. whip antennas, cylindrical coil or helix antennas and planar inverted-F antennas (PIFA). The resonance frequency of an antenna is determined on the basis of its electrical length, which is advantageously xcex/2, 3xcex/8, 5xcex/8 or xcex/4, where. xcex is the wavelength applied. Thus, one and the same basic antenna has in principle several frequency bands that can be used. The drawback, however, is that these frequency bands seldom falls on the bands of the two desired networks. From the prior art it is also known different combined antennas that can function in two frequency ranges: a combined helix and whip antenna, and a combined PIFA and whip antenna, for example. In these solutions the whip antenna, when pulled out, functions at the lower operating frequency and the other part of the antenna construction functions at the upper operating frequency. The disadvantage of the helix-whip combination is the protrusion caused by the helix part which is inconvenient when the communications apparatus is placed in a pocket, for example. The disadvantage of the PIFA-whip combination is that the user""s hand may almost completely cover the PIFA, located inside the housing of the phone, thus considerably degrading the operation of the PIFA.
An object of this invention is to reduce said disadvantages of dual-frequency antennas according to the prior art.
The antenna according to the invention is characterized by what is expressed in the independent claim. Preferred embodiments of the invention are presented in the other claims.
The basic idea of the invention is as follows: A dielectric block with a relatively high permittivity is added to the whip antenna, at a point where there is a voltage maximum at a harmonic frequency of the basic resonance frequency of the antenna. The dielectric medium causes the harmonic frequency in question to shift downwards. The arrangement is realized such that the basic resonance frequency of the whip antenna falls on the operating frequency band of one network and the harmonic frequency in question falls on the operating frequency band of the other network. The construction may further comprise a PIFA that operates in the corresponding operating frequency bands according to the systems.
An advantage of the invention is that a single whip antenna can be used in two desired frequency bands when the antenna is in the pulled-out position. Another advantage of the invention is that when the whip antenna according to the invention is used together with a PIFA, the degradation of the operation of the PIFA caused by the user""s hand will not substantially degrade the connection since the whip, too, operates in the operating frequency of the PIFA. A further advantage of the invention is that the manufacturing costs of the construction according to the invention are relatively low.
The invention will now be described in detail. Reference will be made to the attached drawing wherein
FIG. 1 shows an example of the arrangement according to the invention with one dielectric part in the whip antenna,
FIG. 2 shows an example of the arrangement according to the invention with two dielectric parts in the whip antenna,
FIG. 3 shows an example of the combination of a whip antenna and PIFA in accordance with the invention,
FIG. 4 shows an example of the reflection coefficient of a conventional whip antenna as a function of the frequency, and
FIG. 5 shows an example of the reflection coefficient of the whip antenna according to the invention as a function of the frequency.